/*
 * 
 *   Copyright 2007-2008 University Of Southern California
 * 
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 *   Unless required by applicable law or agreed to in writing,
 *   software distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *   limitations under the License.
 * 
 */
package edu.isi.pegasus.workflowsim.clusering.balancing.metrics;

import edu.isi.pegasus.workflowsim.clusering.balancing.metrics.BalancingMetric;
import edu.isi.pegasus.workflowsim.clusering.TaskSet;
import java.util.ArrayList;

/**
 *
 * @author Weiwei Chen
 */
public class HorizontalRuntimeVariance implements BalancingMetric {
    @Override
    public double getMetric(ArrayList<TaskSet> list){
        if(list == null || list.size() <= 1){
            return 0.0;
        }
        long sum = 0;
        for(TaskSet task: list){
            sum+= task.getJobRuntime();
            //Log.printLine(task.getJobRuntime());
        }
        long mean = sum / list.size();
        sum = 0;
        for(TaskSet task: list){
            long var = task.getJobRuntime();
            sum += Math.pow((double)(var-mean), 2);
        }
        return Math.sqrt((double)(sum/list.size()))/mean;
    } 
}
